The 203rd Engineer Battalion is a combat engineer battalion of the Missouri Army National Guard. The 203rd Engineer Combat Battalion can trace its history back to Missouri volunteer militia units that formed in 1883, when the militia units in southwest Missouri were reorganized into the 2nd Infantry Regiment of the National Guard of Missouri in 1890 and mustered into federal service during the Spanish-American War. The 2nd Missouri Infantry was called up to serve during the Mexican border dispute in 1916; redesigned as 128th, 129th, and 130th machine gun battalions in 1917; transformed into the 203rd Artillery, Coast Artillery Corps in 1921; inducted into federal service in September 1940; and was later sent to Alaska for the Aleutian Campaign.